| Max size | 950 sq ftgross living area |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | No limit |
| Type | Attached or detachedby right in every district |
| Parking | 1 extra spaceplus 1 for the main house |
| Owner-occupancy | Not requiredyou may rent both units |
| Short-term rental | Not stated |
| Utility connection | Tie into the existing electrical connection or choose a separate metersame statewide |
The July 2025 state law (RSA 674:71–73) overrides local ordinance language that conflicts with it — even language a town still has posted. Here's what that means in Boscawen:
Boscawen fixed its ADU article but never touched the lot-size table, which still charges you more land for a second dwelling unit. If the Building Inspector counted your ADU as a second 'unit,' a lot that's big enough for your house could suddenly be declared too small for your ADU. State law forbids that: the town cannot require one square foot more land for a house-plus-ADU than it requires for the house alone. If you get told your lot is too small, that's the one to push back on.
The good news: Boscawen only asks for one extra parking space, which is exactly what state law allows (and the town even cut its general residential standard from 2 spaces to 1 to match). The gap is the other half of the rule — state law says YOU choose whether that space sits on your lot or at a legally dedicated spot off-site. Boscawen's ordinance is written as if the space must be on your property. If squeezing a second space onto your lot is the thing blocking your ADU, state law gives you an off-site option the ordinance doesn't mention.
If you're building a brand-new house and want the ADU in the same project, state law says you can — you don't have to finish the house, wait, and come back. Boscawen's ordinance doesn't say this either way, so a cautious Building Inspector might read it as requiring an existing house first. State law settles it in your favor. This is a silence-in-the-ordinance issue, not the town actively blocking you.
Boscawen is, so far, one of the most homeowner-friendly ADU towns in this dataset — and unusually, that's on purpose.
WHAT THE TOWN ALLOWS. You may build one accessory dwelling unit per lot, attached to or detached from your single-family house (or detached on the lot of a duplex), in EVERY zoning district in Boscawen — AR, R1, R2, Commercial, Industrial, the Mill Redevelopment District, and the Village District. The Table of Uses marks it 'A' straight across, with no district where it's prohibited or requires a conditional use permit. The process is a building permit, full stop: Article XXIII 23.03 says applications 'shall be considered for approval by making a Building Permit Application to the Building Inspector.' No ZBA hearing, no special exception, no Planning Board review, no abutter notice.
THE NUMBERS. Maximum 950 sq ft of gross living area — the full state ceiling. No minimum size. No bedroom limit. No owner-occupancy requirement at all (state law would have LET Boscawen make you live in one of the units; the town chose not to, so you can rent both out). One extra parking space, that's it. A new detached ADU has to meet the ordinary district setbacks (in R2 that's 30 ft front / 10 side / 10 rear; in R1, 40 / 20 / 40; in AR, 50 / 25 / 50) and the ordinary height limit (35 ft in the residential districts). You can rent the ADU, but you cannot sell it off separately — 23.02(f) and (g) bar separate conveyance and condominium conveyance, which is a restriction state law contemplates towns may impose.
THE GARAGE-CONVERSION HEADLINE. This is where Boscawen genuinely outperforms its neighbors. Article XXIII 23.02(h): 'ADUs converted from existing structures, including but not limited to attached garages, are permitted, regardless of whether or not existing structures violate setbacks, dimensional requirements, or lot coverage.' If you have an old garage or outbuilding sitting three feet from the property line, you can convert it. The town even wrote down HOW you prove a structure counts as 'existing' — either it's grandfathered under RSA 674:19, or it previously got a zoning approval or an exemption determination — and you demonstrate that to the Building Inspector. Most NH towns have not caught up to this requirement; Boscawen wrote out the proof mechanism.
WHAT CHANGED, AND WHY IT MATTERS. On March 10, 2026, Boscawen voters passed ten zoning amendments, five of which were aimed squarely at the ADU law. Warrant Article 11 rewrote the entire ADU article 'to reflect the update to the NH State Statutes' (107 yes, 30 no). Warrant Article 5 repealed old Article VI 6.02(c) — the rule that said 'not more than one permanent structure containing residences shall be permitted on a single lot,' which is precisely the clause that had made detached ADUs impossible. Warrant Article 7 cut the residential parking standard from 2 spaces per unit to 1. Warrant Article 9 added formal definitions of 'Accessory Dwelling Unit, Attached' and 'Detached.' Along the way the town deleted a 75%-of-the-primary-dwelling size formula (the kind that shrinks your allowed ADU below the state floor if your house is small) and deleted a rule that had forced every ADU to share the main house's interior access and barred a second exit from facing the street. Do not take the freshness of an ordinance as proof of compliance — Derry amended twice in 2025 and still conflicts, and Candia's '2026 Revision' still mandates a shared street entrance — but in Boscawen's case the reconciliation genuinely came out clean on most points.
WHERE STATE LAW STILL BEATS THE TOWN — THREE THINGS TO KNOW. (1) LOT SIZE. The town rewrote its ADU article but never touched Article V's Table 2, which still requires more land for 'Two Units' than for 'One Unit' in several districts (in AR with water and sewer, 60,000 sq ft instead of 40,000; in R2 with both, 20,000 instead of 10,000). If anyone tells you your lot is too small for an ADU, state law is explicit: the town may not impose ANY additional lot-size requirement 'beyond what would be required for a single-family dwelling without an accessory dwelling unit.' Your house-sized lot is, by law, an ADU-sized lot. (2) OFF-SITE PARKING. Boscawen asks for one extra space and frames it as an on-lot, off-street space. State law says the required space 'may be provided either on-site or at a legally dedicated off-site location, at the property owner's discretion.' If the only thing standing between you and an ADU is nowhere to put a second car, you have an option the ordinance doesn't mention. (3) BUILDING IT ALL AT ONCE. The ordinance is written as though there's already a house on the lot. State law says you may construct the ADU at the same time as the principal dwelling — you don't have to build the house, wait, and come back for a second permit.
BOTTOM LINE. In Boscawen, the honest answer for most homeowners is: yes, you can build it, you can build it detached, you can convert the garage even if it's too close to the line, you don't have to live there, and you need one permit from one official. The friction points that remain are gaps in the town's OTHER articles rather than restrictions in the ADU article itself — and on every one of those gaps, the state law lands on the homeowner's side.
Primary source: Town zoning ordinance (PDF) — 2026-03-10
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Get My Free Boscawen ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Boscawen's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Boscawen allows one accessory dwelling unit, attached OR detached, BY RIGHT in every single zoning district in town, with nothing more than a building permit from the Building Inspector. Under RSA 674:72 (as amended effective July 1, 2025), one accessory dwelling unit — attached or detached — is allowed by right on single-family lots statewide.
950 sq ft — gross living area. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (by right in every district). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 extra space — plus 1 for the main house. State law caps what any town can require at one additional space, located on- or off-site at the owner's choice.
Not required — you may rent both units. Where owner-occupancy is required, state law lets the owner choose which unit to live in.